1. Field of the Invention
The present invention relates to a method for connecting an a optical waveguide and an optical semiconductor device and an apparatus for connecting the same, particularly to an improvement of a passive alignment system.
2. Description of the Prior Arts
There has existed an electric-optical conversion device called an optical module, which is constituted by integrating an optical semiconductor device such as a semiconductor laser diode and an optical waveguide such as an optical fiber.
In fabricating the optical module, it is an important challenge to allow an emitted light from the optical semiconductor device to be incident onto the optical waveguide with minimal waste and to increase optical coupling coefficiency.
As methods to connecting the optical semiconductor device and the optical waveguide, there have existed an active alignment method and a passive alignment method.
The active alignment method is the one performed as follows. Specifically, an optical semiconductor device is actually made to emit a light and the emitted light is incident onto an optical waveguide. Relative positions of the optical semiconductor device and the optical waveguide with respect to each other are finely adjusted so as to maximize an intensity of the emitted light from the optical waveguide, thus connecting the optical semiconductor device and the optical waveguide.
On the other hand, the passive alignment method is performed as follows. Specifically, the optical semiconductor device is actually not made to emit a light, but alignment marks previously formed in both of the optical semiconductor device and the optical waveguide are made to be coincident with each other. Thus finely adjusting the relative positions of the optical semiconductor device and the optical waveguide with respect to each other to connect them.
In Japanese Patent Laid-Open No. Hei 7 (1995)-43565, published on Feb. 14, 1995, a method to connect the optical waveguide and the optical semiconductor device using the passive alignment method is disclosed. A technology written in the gazette will be described as a first conventional example.
FIG. 10 is a perspective view showing a method for connecting an optical waveguide and an optical semiconductor device of the first conventional example.
In FIG. 10, an optical semiconductor device 102 is loaded onto a sub substrate 101. A thin film for shielding infrared ray is formed entirely on an overall bottom surface 102a of the optical semiconductor device 102 other than regions of markers 161 and 162. The sub substrate 101 has a thin film for shielding infrared ray only at regions of markers 131 and 132, and accommodates an optical fiber 104 in its V-shaped groove 105.
Next, the infrared ray (not shown) is made to transmit through the sub substrate 101 upward from an infrared ray source (not shown) provided below the sub substrate 101, and the markers 131, 132, 161 and 162 are photographed by an infrared ray camera (not shown) provided above the sub substrate 101.
FIG. 11 is a schematic view showing a photographed image in the first conventional connection method.
In FIG. 11, the photographed image of the markers 131, 132, 161 and 162 undergoes an image processing, and relative positions of the optical semiconductor device 102 and the sub substrate 101 with respect to each other are corrected so that areal centers of gravity of the markers 131 and 132 and areal centers of gravity of the markers 161 and 162 are coincident with each other. Thereafter, the optical semiconductor device 102 is loaded onto the sub substrate 101 and jointed to the sub substrate 101, whereby a precision in the connection of the optical semiconductor device 102 and the optical fiber 104 is increased.
Moreover, in Japanese Patent Laid-Open No. Hei 8 (1996)-111600, published on Apr. 30, 1996, a high precision mounting method using a passive alignment method for controlling relative positions of an optical semiconductor device and an optical waveguide based on an overlapping state of polygonal markers is disclosed. A technology written in the gazette is described as a second conventional example.
FIG. 12 is a perspective view showing a method for connecting an optical waveguide and an optical semiconductor device of a second conventional example.
In FIG. 12, an optical semiconductor device 228 is loaded onto a silicon substrate 225. In the optical semiconductor device 228, first markers having parallelogram-shape which allow an infrared ray R (FIG. 13) to transmit through are perforated, and second markers 238 are formed on a bottom surface. An infrared ray R is shielded in other regions than the region of the markers 238. In the silicon substrate 225, a rectangular-shaped holes, which allows the infrared ray R to transmit through, are perforated, and first markers 237 are formed. The infrared ray R is shielded in other regions than the region of the markers 237.
FIG. 13 is a perspective view showing an apparatus for connecting the optical waveguide and the optical semiconductor device of the second conventional example.
In FIG. 13, the infrared ray R is irradiated upward from an infrared-ray source 222 located below the silicon substrate 225 and the optical semiconductor device 228, and an image of the infrared ray R having transmitted through the silicon substrate 225 and the optical semiconductor device 228 is photographed by an infrared-ray camera 231.
FIG. 14 is a schematic view showing an infrared-ray-photographed image in the method for connecting the optical guide and the optical semiconductor device of the second conventional example.
Based on the photographed image as shown in FIG. 14, a deviation of the first and second markers 236 and 238 from each other is obtained, and a parts-moving stage 226 (FIG. 13) and a substrate moving stage 223 (FIG. 13) are controlled so as to make coincident the first and second markers 236 and 238 with each other, thus positioning the silicon substrate 225 and the optical semiconductor device 228.
Moreover, the image of the infrared ray R having transmitted through the first and second markers 236 and 238 is taken out by a half mirror 233 (FIG. 13), and measured by an optical intensity detector 235 (FIG. 13). The silicon substrate 225 and the optical semiconductor device 228 are fixed at a position where an intensity of the image comes to be maximum or minimum, whereby a positioning precision of the silicon substrate 225 and the optical semiconductor device 228 is increased.
As a still another conventional example, in Japanese Patent Laid-Open No. Hei 9 (1997)-205255, published on Aug. 5, 1997, an optical semiconductor device using an passive alignment method, in which areal centers of gravity of alignment marks provided respectively on a semiconductor laser chip and a sub-mount are made to be coincident with each other, and a method for manufacturing the same are disclosed.
Moreover, in Japanese Patent Laid-Open No. Hei 9 (1997)-292542, published on Nov. 11, 1997, an optical part mounting substrate using a passive alignment method, in which alignment marks provided respectively on a semiconductor laser chip and an optical part fixing member are detected thus mounting one on another, is disclosed.
However, the connection methods for the optical waveguide and the optical semiconductor device in the conventional examples have the following problems.
In the first conventional example shown in FIG. 10, when a working error exists on an outgoing surface 102b of the optical semiconductor device 102, a distance from the outgoing surface 102b of the optical semiconductor device 102 to an incident surface 104a of the optical fiber 104 shifts from a designed distance. Thus, an optical coupling coefficiency of the optical semiconductor device 102 and the optical fiber 104 reduces.
The reason is as follows. Specifically, when the optical semiconductor device 102 such as a laser diode is manufactured, after markers 161 and 162 are formed, the outgoing surface 102b is formed by performing a cleavage processing for the optical semiconductor device 102. Since this cleavage processing is performed in such manner that a breakable semiconductor is split so as to obtain the outgoing surface 102b, a working error of the outgoing surface 102b with respect to the markers 161 and 162 cannot be made to be 10 xcexcm or less. On the other hand, in the case of the optical semiconductor device 102 for which a high optical output power and a high optical coupling coefficiency are needed, a distance from the outgoing surface 102b of the optical semiconductor device 102 to the incident surface 104a of the optical fiber 104 must be reduced to about 3 xcexcm. It is nevertheless difficult to meet the requirement as long as the cleavage processing is adopted.
Moreover, the distance from the outgoing surface 102b of the optical semiconductor device 102 to the incident surface 104a of the optical fiber 104 cannot be obtained as designed, and there is a problem that the optical coupling coefficiency is low.
The reason is as follows. Specifically, if a slit 110 for deciding the position of an incident surface 107a of a sub substrate 107 is formed by grinding the sub substrate 107 in a mechanical working manner, a working error of 5 xcexcm or more is created. Similarly, even if the incident surface 104a of the optical fiber 104 is polished so as to smooth it using a blade saw, the working error of 5 xcexcm or more is created. Specifically, the working error of 10 xcexcm or more in total exists.
There have been these problems in any of the foregoing conventional examples.
Any of the foregoing conventional examples discloses simply the technology in which the areal center of gravity of the alignment marks are made to be coincident with each other, or the technology in which the positioning is controlled based on the overlapping state of the alignment markers. When the foregoing working error of the outgoing surface exists or the foregoing working error of the incident surface exists, any of the foregoing conventional examples cannot aim at removing the working errors, and does not disclose concrete method to remove the working errors.
Accordingly, any of the foregoing conventional examples cannot remove the foregoing working errors in principle.
The object of the present invention is to provide a method for connecting an optical waveguide and an optical semiconductor device and an apparatus for connecting the optical waveguide and the optical semiconductor device, capable of removing a working error and getting a high optical coupling coefficiency.
A first aspect of the method is that: a method for connecting an optical waveguide for guiding light and an optical semiconductor device having an outgoing surface for emitting the light, the optical waveguide being formed in a first region on a top surface of a substrate, on which a pair of first positioning marks are formed for transmitting or shielding an infrared ray only at specified spots in a second region adjacent to the first region, and the optical semiconductor device having a bottom surface on which a pair of second positioning marks for transmitting or shielding the infrared ray are formed thereof, the second positioning marks being concentric and having a different diameter from that of the first positioning marks and an inverted pattern shape to that of the first positioning marks. The method consisting of the steps of: moving the optical semiconductor device to the substrate so as to overlap the pair of the first positioning marks and the pair of the second positioning marks; obtaining an actual distance from the outgoing surface to the pair of the second positioning marks, based on an image photographed by allowing the infrared ray to transmit through the substrate and the optical semiconductor device; obtaining an error between the actual distance and a designed distance previously set, by subtracting the designed distance between the outgoing surface of the optical semiconductor device and the pair of the second positioning marks from the actual distance; moving the pair of the second positioning marks relative to the pair of the first positioning marks by a quantity equal to the error so as to cancel the error; and jointing the optical semiconductor device to the substrate.
A second aspect of a method is that: a method for connecting an optical waveguide and an optical semiconductor device, the optical waveguide being laid in a groove formed on a top surface of a substrate on which a pair of first positioning marks are formed for transmitting or shielding an infrared ray only at specified spots and having one end surface thrusted to a thrust end surface, that is one end of the groove, so as to be positioned, and the optical semiconductor device having a bottom surface, in which a pair of second positioning marks for transmitting or shielding the infrared ray are formed, the second positioning marks being concentric and having a different diameter from that of the first positioning marks and an inverted pattern shape to that of the first positioning marks. The method consisting of the steps of: moving the optical semiconductor device to the substrate so as to overlap the pair of the first positioning marks and the pair of the second positioning marks; obtaining an actual distance from an outgoing surface of the optical semiconductor device to the thrust end surface, based on an image photographed by allowing the infrared ray to transmit through the substrate and the optical semiconductor device; obtaining an error between the actual distance and a designed distance previously set, by subtracting the designed distance between the outgoing surface of the optical semiconductor device and the thrust end surface of the slit from the actual distance; moving the pair of the second positioning marks relative to the pair of the first positioning marks by a quantity equal to the error so as to cancel the error; and jointing the optical semiconductor device to the substrate.
A first aspect of the apparatus is that: an apparatus for connecting an optical waveguide for guiding light and an optical semiconductor device having an outgoing surface for emitting the light, the optical waveguide being formed in a first region on a top surface of a substrate, on which a pair of first positioning marks are formed for transmitting or shielding an infrared ray only at specified spots in a second region adjacent to the first region, and the optical semiconductor device having a bottom surface on which a pair of second positioning marks for transmitting or shielding the infrared ray are formed thereof, the second positioning marks being concentric and having a different diameter from that of the first positioning marks and an inverted pattern shape to that of the first positioning marks. The apparatus consisting of: a stage for moving relatively the substrate and the optical semiconductor device; a light source for irradiating the infrared ray; a camera for photographing an image formed by the infrared ray irradiated from the light source and transmitted through the substrate and the optical semiconductor device; and a control unit for controlling the stage based on the image from the camera. The control unit drives the stage so as to overlap the pair of the first positioning marks and the pair of the second positioning marks; obtains an actual distance from the outgoing surface to the pair of the second positioning marks, based on the image photographed from the camera; obtains an error between the actual distance and a designed distance previously set, by subtracting the designed distance between the outgoing surface of the optical semiconductor device and the pair of the second positioning marks from the actual distance; and moves the pair of the second positioning marks relative to the pair of the first positioning marks by driving the stage by a quantity equal to the error so as to cancel the error.
A second aspect of an apparatus is that: an apparatus for connecting an optical waveguide and an optical semiconductor device, the optical waveguide being laid in a groove formed on a top surface of a substrate on which a pair of first positioning marks are formed for transmitting or shielding an infrared ray only at specified spots and having one end surface thrusted to a thrust end surface, that is one end of the groove, so as to be positioned, and the optical semiconductor device having a bottom surface, in which a pair of second positioning marks for transmitting or shielding the infrared ray are formed, the second positioning marks being concentric and having a different diameter from that of the first positioning marks and an inverted pattern shape to that of the first positioning marks. The apparatus consisting of: a stage for moving relatively the substrate and the optical semiconductor device; a light source for irradiating the infrared ray; a camera for photographing an image formed by the infrared ray irradiated from the light source and transmitted through the substrate and the optical semiconductor device; and a control unit for controlling the stage based on the image from the camera. The control unit drives the stage so as to overlap the pair of the first positioning marks and the pair of the second positioning marks; obtains an actual distance from the pair of the second positioning marks to the thrust end surface, based on the image from the camera; obtains an error between the actual distance and a designed distance previously set, by subtracting the designed distance between the pair of the second positioning marks of the optical semiconductor device and the thrust end surface of the slit from the actual distance, and moves the pair of the second positioning marks relative to the pair of the first positioning marks by driving the stage by a quantity equal to the error so as to cancel the error.
In the conventional examples, the relative positions of the substrate and the optical semiconductor device are controlled so that first and second positioning marks are made to be simply coincident with each other. Compared to the conventional examples, according to the methods and the apparatuses of the present invention as described above, the present invention is characterized as follows. The first and second positioning marks are once overlapped, and the actual distance from the positioning mark of the optical semiconductor device to either the outgoing surface of the optical semiconductor device or the thrust end surface of the slit of the substrate is measured. Then an error is obtained by subtracting a designed distance previously set from the actual distance obtained, and the optical semiconductor device is moved by the quantity equal to the error so as to cancel the error, thus jointing the optical semiconductor device to the optical waveguide substrate.
Since the constitutions and the technique described above are adopted in the present invention, the distance between the outgoing surface of the optical semiconductor device and the incident surface of the optical waveguide can be always made to be coincident wits the designed distance precisely.